The popularity of snack food products such as potato chips is well known and had become a significant contributor to the calories and fats consumed in a day by the consuming public. The manufacturers of snack food products have become very much aware of this dietary concern by the consuming public and have responded by introducing low fat potato chips having a fat content from 0% to 27%. The processes employed include using a microwave oven in combination with conventional radiant heat forced air type of oven, as well as infrared energy. The most comprehensive teachings in the field of the present invention can be found in U.S. Pat. No. 4,800,090 to August. The patent teaches the preparation of a potato chip without the use of oil, using first an infrared heating source to warm the exterior of the sliced potato pieces, then a microwave energy source to warm the interior of the potato pieces and finally a second infrared heating source to achieve browning of the potato pieces. The infrared energy is supplied evidently at a relatively low intensity in that the exposure time for precooking can be as long as 5 minutes. This is followed by microwave treatment for as long as 5 minutes with a preferable range at one to two minutes. The final infrared browning stage is in the preferable range of about one minute although the range may be as long as 5 minutes. The overall cook time in the August '090 patent is quite long. The electrical energy consumption in the microwave cooking step is high and the energy consumption in the infrared stages should ideally be reduced. The desired layering or blistering of the potato product is not seen as easily obtained in the teachings of the August '090 patent as is desired in the marketplace by consumers.
The usual method of preparing potato chips involves the slicing of raw potatoes, the insertion of these slices into a reservoir of hot oil for a predetermined period of time so that the slices are fried to a crisp state, followed by the removal of the fried chips from the oil. The effect of frying of the potato slices is to reduce the water content of the slices while allowing the undesirable oil uptake. The oil uptake however results in the appropriate surface color while the reduction of the water content causes the desired crispness. Fresh potatoes contain approximately 80% moisture. The finished potato chip product contains less than 2% moisture. The oil fried chips contain from 30-40% oil or fat of the total weight of the potato chip.